The pathway of AMP degradation in prokaryotic organisms involves hydrolysis of the N-glycosidic bond of AMP nucleosidase. The enzyme activity in vitro is allosterically regulated by MgATP2 minus activation, Pi inhibition and by a Pi mediated, reversible dissociation to form inactive enzyme subunits. The pathway for AMP degradation in eukaryotic organisms including yeast and mammalian tissues appears to involve hydrolysis of the amino group from AMP by AMP deaminase. AMP deaminase is an allosteric enzyme which is also regulated by MgATP2 minus activation and Pi inhibition. In a number of organisms thus far examined, none have been found to contain both the AMP nucleosidase and AMP deaminase. The similarity of the catalytic and regulatory properties and the common metabolic action of these two enzymes suggest that AMP deaminase may have evolved from AMP nucleosidase. The metabolic role of AMP nucleosidase will be investigated by the study of adenylate metabolism in Azotobacter vinelandii mutants which lack this enzyme. The proposal that AMP nucleosidase and AMP deaminase are related proteins will be investigated by comparative protein structure analysis. A limited amino acid sequence determination using AMP deaminase from bakers yeast and AMP nucleosidase from A. vinelandii will be used to provide information on the structure and homology of these functionally related proteins. The regulatory properties of yeast AMP deaminase will be studied by steady-state kinetic methods.